The title size is dictated by the title hierarchy (H1 … H6) which is why the sizes are fixed; the underline, in turn, is a part of the theme’s design – this is why those two parameters are not directly adjustable via the admin back-end settings. However, you can override the above by using a piece of custom CSS:
You can insert it via a child theme or by using the “Style: Add Custom CSS” tab of the Theme Options panel.
Regarding your second question – as far as I can see in the code, you are using the “Blog Posts” page template for the part of the one-page view which displays the news (this is the source page for that section), while its content is represented by a series of plain-text paragraphs. I’d advise switching the template for that page to “Page: Right Sidebar” or “Page: Full-Width”, which will serve your purpose just as well given your current setup, and will remove the “See All” button on the one-page view.